Sim (simulated) racing is the collective term for computer software that attempts to accurately simulate auto racing, complete with real-world variables such as fuel usage, damage, tire wear and grip, and suspension settings. To be competitive in sim racing, a driver must understand all aspects of car handling that make real-world racing so difficult, such as threshold braking, how to maintain control of a car as the tires lose traction, and how properly to enter and exit a turn without sacrificing speed. It is this level of difficulty that distinguishes sim racing from "arcade" driving games where real-world variables are taken out of the equation and the principal objective is to create a sense of speed as opposed to a sense of realism.
In general, sim racing applications, such as rFactor, Grand Prix Legends, Race 07, F1 Challenge '99-'02, Assetto Corsa, rFactor 2, GTR 2 and iRacing are less popular than arcade-style games, mainly because much more skill and practice is required to master them. However, sims such as 'NASCAR Racing 2003 Season and Richard Burns Rally have achieved worldwide fame. Also, because of the demands on the computer system, race sims require faster computers to run effectively, as well as a somewhat costly steering wheel and pedals for the throttle and brakes. Most arcade-style driving games can be played with a simple joystick controller or even a mouse and keyboard.
With the development of online racing capability, the ability to drive against human opponents as opposed to computer AI is the closest many will come to driving real cars on a real track. Even those who race in real-world competition use simulations for practice or for entertainment. With continued development of the physics engine software that forms the basis of these sims, as well as improved hardware (providing tactile feedback), the experience is becoming more realistic.